KR20060100693A - Back-light unit of liquid crystal display device - Google Patents

Abstract

The present invention relates to a backlight unit of a liquid crystal display device capable of reducing power consumption, comprising: a lamp for emitting light; An inverter which converts an input power source into an alternating current, transforms it, and supplies the lamp to the lamp; By periodically charging and discharging the current supplied to the inverter, it is composed of an energy reuse unit for raising the voltage applied to the inverter to a desired level without supplying external current.

LC resonance, power consumption, charge, discharge, lamp, current

Description

BACK-LIGHT UNIT OF LIQUID CRYSTAL DISPLAY DEVICE}

1 is a view showing a backlight unit according to the present invention.

FIG. 2 shows waveforms of the a-b voltage of FIG. 1; FIG.

*** Description of the symbols for the main parts of the drawings ***

10: inverter 15: transformer

20: energy reuse section 30: lamp

Vin: input voltage D1: first diode

D2: second diode T1: first transistor

T2: second transistor T3: third transistor

T4: fourth transistor CS1: first control signal

CS2: second control signal CS3: third control signal

CS4: fourth control signal C1: first capacitor

C2: second capacitor C3: third capacitor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back-light unit of a liquid crystal display device, and in particular, to reduce power consumption by recharging and reusing the power supplied for driving a lamp. It relates to a backlight unit of a liquid crystal display device that can reduce the.

Recently, with the development of information technology, various display apparatuses for visually implementing information have been developed. In particular, the liquid crystal display is a next generation display device capable of realizing thin, light, low power consumption and clear image quality, and is rapidly replacing a cathode ray tube (CRT), which is widely used in the related art.

A liquid crystal display device is a display device using optical anisotropy of liquid crystals. A liquid crystal is rearranged and supplied from a light source by applying a constant electric field to a liquid crystal injected between a thin film transistor array substrate and a color filter substrate. It is characterized by displaying an image by adjusting the transmittance of light to be produced.

The liquid crystal display device includes a liquid crystal panel in which a liquid crystal is injected between the thin film transistor array substrate and the color filter substrate, a driver for driving the liquid crystal panel, and supplying light to the liquid crystal panel. It is divided into a backlight unit.

The backlight unit includes an inverter that receives an external DC power supply and converts the same into a high voltage AC, and a lamp that is driven by an AC supplied from the inverter to emit light. Metal electrodes are provided at both ends of the lamp, and a gas is filled in the lamp, and mercury gas is usually filled.

The driving of the backlight unit configured as described above is as follows. When a high voltage is applied across the lamp, free electrons protrude from the metal electrode to bring the gas into an excited state, and the gas is returned to a stable state, and the emitted ultraviolet rays react with the fluorescent material applied to the inner wall of the lamp. Light emission occurs.

As described above, in order to raise the voltage across the lamp to a high level to cause the initial reaction of the lamp, a large amount of current must be supplied to the lamp, and in order to continue to emit the lamp that has started to drive when discharge is triggered. The current must be supplied.

Due to such driving characteristics, the backlight unit requires more power consumption than other devices in the liquid crystal display. In recent years, as the number of lamps mounted for the purpose of improving the brightness of liquid crystal displays increases, the power consumption required for the backlight unit also increases gradually.

The present invention was devised to solve the conventional problems as described above, and an object of the present invention is to charge a part of the power supplied to the inverter for lamp driving purposes and reuse it to drive the lamp, thereby further reducing the power to be supplied. The present invention provides a backlight unit of a liquid crystal display device.

A backlight unit of a liquid crystal display device for achieving the object of the present invention includes a lamp for emitting light; An inverter which converts an input power source into an alternating current, transforms the power supply, and supplies it to the lamp; It is composed of an energy reuse unit for periodically charging and discharging the current supplied to the inverter to increase the voltage applied to the inverter to a desired level without supplying an external current.

1 is a view showing a backlight unit of a liquid crystal display according to the present invention.

1, a lamp 14 for emitting light; An inverter (10) which alternately switches an input voltage (Vin) to convert to an alternating current, and boosts the converted alternating current to supply it to the lamp (14); And an energy reuse unit 20 for charging a part of the input voltage Vin supplied to the inverter 10 and discharging the charged voltage to supply the inverter 10.

The first transistor T1 and the second transistor T2 provided in the inverter 10 are connected in series, and the second capacitor C2 is common to the first transistor T1 and the second transistor T2. Is connected. Then, both sides of the primary coil of the transformer 15 are connected to the second capacitor C2 and the second transistor T2, respectively.

The primary coil and the secondary coil of the transformer 15 have a turn ratio of N1: N2, and the secondary coil is connected in parallel with the first capacitor C1 and the lamp 30. Here, since N1 and N2 are natural numbers, and the transformer 15 is for the purpose of boosting, N2 should be made larger than N1. The first inductor (L1) is represented by shaping the leakage inductance (leakage inductance) of the transformer (15). The transformer 15 together with the first capacitor C1 resonates the voltage level induced from the primary coil to the secondary coil of the transformer 15 so that a higher level voltage is applied to the lamp 30. do.

The energy reuse unit 20 electrically connected to the inverter 10 includes a first diode D1 and a second diode D2 connected in series, and a third transistor connected to an anode electrode of the first diode D1. T3), a fourth transistor T4 connected to the cathode electrode of the second diode D2, and a third capacitor C3 commonly connected to the third and fourth transistors T3 and T4.

Electrodes opposite to each other are connected to the first diode D1 and the second diode D2. That is, the first diode D1 and the second diode D2 are connected to the inverter 10 in the forward and reverse directions, respectively, so that the current between the inverter 10 and the energy reuse unit 20 only through one of them. Restrict flow.

The first to fourth transistors T1 to T4 included in the backlight unit are turned on or turned off by the first to fourth control signals CS1 to CS4, respectively.

The input voltage Vin applied to the inverter 10 is a DC voltage. The input voltage Vin is applied to the inverter 10 through the first transistor T1 and alternately turned on by the first and second control signals CS1 and CS2. T1 and T2) periodically swing the high potential and low potential levels. Nodes a and b shown in the figure are reference nodes arbitrarily set in order to easily explain the input voltage Vin applied to the inverter 10. The node b is ground, and the voltage a-b, which is the voltage difference between the node a and the node b, indicates the level of the input voltage Vin applied to the inverter 10.

The a-b voltage is periodically transitioned to the high potential or the low potential by the first and second transistors T1 and T2 alternately turned on. The second capacitor C2 included in the inverter 10 is provided to cut off the DC component of the voltage, and the second capacitor C2 blocks the DC component included in the ab voltage. The voltage applied to the primary coil of) is an AC voltage having the same amplitude as the ab voltage. The current supplied to the primary coil of the transformer 15 is supplied with alternating current according to the operation of the second capacitor C2.

The AC component of the a-b voltage applied to the primary coil of the transformer 15 is transformed according to the turn ratio of the primary coil and the secondary coil and induced in the secondary coil. However, since the number of turns of the secondary coil is greater than that of the primary coil, the transformer 15 has a higher voltage than the voltage applied to the primary coil.

On the other hand, in the primary coil of the transformer 15, flux is generated according to the change of the current flowing through the primary coil, and the current is induced in the secondary coil by linking with the secondary coil. However, some of the magnetic fluxes linking from the primary coil to the secondary coil are leaked, and the inductance caused by the leakage flux is represented by the first inductor L1. The first inductor L1 generates an LC resonant and a first capacitor C1 connected in parallel with the lamp 30 to convert the high voltage induced in the secondary coil of the transformer 15 into a higher voltage. Raise. Since the lamp 30 is initially discharged and starts to emit light, a high voltage of several thousand V is usually required, so that the lamp 30 is boosted to a voltage sufficient to initially drive the lamp 30 through the transformer and LC resonance.

The driving of the backlight unit to which the energy reuse unit 20 is connected will be described in detail with reference to the voltage waveform of FIG. 2.

The driving process of the backlight unit of the present invention can be divided into four steps according to the waveform of the a-b voltage shown in FIG. 2.

First, in the first step, the first transistor T1 is turned on by the first control signal CS1 so that the current flows into the inverter 10 so that the ab voltage rises to the same level as the input voltage Vin. The same potential state is maintained for a predetermined time. When the lamp 30 starts to discharge due to a high voltage and emits light, the lamp 30 continuously draws current from the inverter 10 to replenish the charge for maintaining the discharge state. Therefore, the current supplied to the inverter 10 from the outside is consumed to drive the lamp 30, the level of the a-b voltage is lowered. However, since the discharge of the lamp 30 may be stopped when the a-b voltage level drops, the inverter 10 receives an additional current from the outside to maintain the a-b voltage level.

As described above, in the first transistor T1 turn-on period, the a-b voltage maintains the level of the input voltage Vin, and the lamp 30 emits light. At this time, if only the voltage of the same polarity induced in the secondary coil of the transformer 15 is continuously applied to both ends of the lamp 30, the polarization is completed inside the lamp 30 after a certain time, the discharge no longer occurs. Will not. Therefore, it is necessary to change the polarity of the voltage across the lamp 30 to continue to discharge. That is, since the lamp 30 is an element driven by an alternating current, it is necessary to apply alternating current through the transformer 15.

The first transistor T1 and the second transistor T2 are alternately turned on to generate alternating current. For example, when the first transistor T1 is turned off and the second transistor T2 is turned on, the a-b voltage drops to 0V. On the contrary, when the first transistor T1 is turned on and the second transistor T2 is turned off, the a-b voltage becomes the input voltage Vin level. That is, under the control of the first transistor T1 and the second transistor T2, the a-b voltage becomes a square wave type that transitions between two levels. However, even when the second transistor T2 is turned on, the electric charge supplied to drive the lamp 30 remains in the inverter 10. The ab voltage still maintains the input voltage Vin level. Keeping up. Therefore, a new step is included that can be reused for driving the lamps that are periodically repeated by charging the a-b voltage of the inverter 10.

The second step of driving the backlight unit is charging the energy reuse unit 20 with the a-b voltage of the inverter 10.

In order to raise the a-b voltage to the level of the input voltage Vin, much current must be supplied to the inverter 10. Accordingly, a large amount of power is consumed by the inverter 10 every time the first transistor T1 is turned on. In the present invention, by storing the charge supplied to the inverter 10 in the first transistor (T1) turn-on period and reuse in the next turn-on period of the first transistor (T1), the energy that is reused is the By replacing a portion, it is possible to reduce the current to be additionally supplied from the outside.

In the second step, only the fourth transistor T4 of the energy reuse unit 20 is turned on. Accordingly, an electrical path is formed between the inverter 10 and the energy reuse unit 20 to connect a node, the first diode D1, the fourth transistor T4, and the third capacitor C3. A current is supplied from the inverter 10 to the energy reuse unit 20 through a path, and a constant voltage is charged to the third capacitor C3. The ab voltage waveform is subjected to LC resonance as shown in the waveform shown in FIG. 2 by the action of the capacitance of the third capacitor C3 and the leakage inductance of the transformer 15, so that the time for the voltage drop is delayed. The third capacitor C3 may be supplied with sufficient charge to charge the voltage to a desired level. The desired level will be the voltage level that causes the discharge of the lamp to begin initial drive. More specifically, since the voltage of the inverter 10 is boosted once through the transformer 15 and supplied to the lamp, a voltage for boosting and initially driving the lamp should be applied to the primary coil of the transformer 15.

Since the voltage charged in the third capacitor C3 is discharged afterwards, the voltage magnitude is boosted twice by LC resonance, so that only one half of the input voltage Vin is charged in the third capacitor C3. .

On the other hand, the second diode (D2) is connected to the current flowing from the inverter 10 in the reverse direction to block the current flow, the voltage is charged to the third capacitor (C3) only through the first diode (D1). do.

Sufficient voltage is charged in the third capacitor C3, and the fourth transistor T4 is turned off. In the third step of driving the backlight unit, the fourth transistor T4 is turned off and the second transistor T2 is turned on.

As the fourth transistor T2 is turned off, the energy reuse unit 20 is electrically cut off from the inverter 10 so that the third capacitor C3 maintains the charged voltage.

On the other hand, since the node a and the node b which is the ground are connected through the turned-on second transistor T2 of the inverter 10, the node a becomes the base voltage level. At this time, the direction of the current flowing in the primary coil of the transformer 15 is reversed in the first step in which the first transistor T1 is turned on. Therefore, the lamp 30 emits light continuously without interruption of discharge.

When the first stage again, the second transistor T2 of the inverter 10 is turned off, and the third transistor T3 of the energy reuse unit 20 is turned on. Therefore, while the voltage charged in the third capacitor C3 is discharged, the voltage a-b of the inverter 10 is increased. At this time, the ab voltage is LC-resonated by the leakage inductance of the third capacitor (C3) and the transformer 15 to increase to the input voltage (Vin) level, the third capacitor (C3) without supplying additional current from the outside Raise the ab voltage level only with the voltage discharged at.

Since the ab voltage is previously raised to a voltage level capable of initially driving the lamp 30 only by the charging voltage of the third capacitor C3 of the energy reuse unit 20, the first transistor T1 is turned on. In the second step, only the minimum current to maintain the ab voltage level needs to be additionally supplied. That is, the power consumed by the backlight unit can be reduced.

Recently, when the number of lamps 30 mounted in a liquid crystal display device gradually increasing the panel area increases, the power reuse unit 20 as described above is provided when the power for driving the lamp 30 is increased. If the voltage of 10) is charged and reused, power consumption may be greatly reduced.

As described above, the backlight unit of the liquid crystal display according to the present invention can reduce the amount of current to be additionally supplied from the outside by charging the supplied voltage for driving the lamp and reusing the lamp to reduce the power consumption of the liquid crystal display. have.

Claims (10)

A lamp for emitting light; An inverter converting an input power into an alternating current, transforming the power supply, and supplying the converted power to the lamp; And an energy reuse unit for periodically charging and discharging the current supplied to the inverter to raise the voltage of the inverter to a level capable of driving the lamp. The method of claim 1, wherein the inverter First and second transistors which alternately conduct or block input power to generate a pulse voltage; A capacitor for selectively passing only an alternating current component among voltages generated by the first and second transistors; And a transformer for boosting the AC component transmitted through the first capacitor and applying the voltage to the lamp. The backlight unit of claim 1, wherein an additional current is supplied from the outside after the voltage of the inverter reaches a desired level by the voltage discharged from the energy reuse unit. 4. The backlight unit of claim 3, wherein the external current supplied to the inverter is a minimum current for maintaining the voltage level of the inverter. The method of claim 1, wherein the energy reuse unit A second capacitor charging the voltage applied to the inverter or discharging the charged voltage to the inverter; A first diode and a fourth transistor configured to pass the voltage of the inverter and transfer the voltage to the second capacitor; And a second diode and a third transistor configured to transfer the voltage discharged from the second capacitor to the inverter. 6. The backlight unit of claim 5, wherein one of the first diode and the second diode is disposed in a forward direction with respect to the voltage polarity applied to the inverter, and the other is disposed in a reverse direction. The backlight unit of claim 5, wherein the voltage charged in the capacitor is smaller than an input voltage applied to the inverter. The backlight unit of claim 5, wherein the voltage charged in the capacitor is 1/2 of an input voltage of the inverter. The backlight unit of claim 1, wherein LC resonance occurs when the voltage of the inverter is charged in the energy reuse part or the voltage charged in the energy reuse part is discharged by the inverter. The backlight unit of claim 9, wherein the LC resonance is generated by a capacitance of a capacitor of the energy reuse unit and a leakage inductance of a transformer of the inverter.

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